1. Field of the Invention
The present invention relates to hermetically sealed glass packages that are suitable to protect thin film devices which are sensitive to the ambient environment. Some examples of such glass packages are organic light emitting diode (OLED) displays, sensors, photovoltaics and other optical devices. The present invention is demonstrated using an OLED display as an example.
2. Description of Related Art
OLEDs have been the subject of a considerable amount of research in recent years because of their use and potential use in a wide variety of electroluminescent devices. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting applications or flat-panel display applications (e.g., OLED displays). OLED displays are known to be very bright and to have a good color contrast and wide viewing angle. On the other hand, however, OLED displays, and in particular the electrodes and organic layers located therein, are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. The life of an OLED display can be significantly increased if the electrodes and organic layers located therein are hermetically sealed from the ambient environment. Unfortunately, it has been very difficult to develop a sealing process to hermetically seal the OLED display. Some of the factors that have made it difficult to properly seal the OLED display are briefly mentioned below:                The hermetic seal should provide a barrier for oxygen (10−3 cc/m2/day) and water (10−6 g/m2/day);        The hermetic seal should survive mechanical shocks, such as those generated when a cell phone falls to the ground, received during the use of the display;        The width of the hermetic seal should be small (e.g., <2 mm) so that it does not have an adverse effect on the size of the OLED display;        The temperature generated during a sealing process should not damage the materials (e.g., electrodes and organic layers) within the OLED display. For instance, in a typical OLED display, the first pixels of OLEDs are located close to the hermetic seal and should not be heated to more than about 85-100° C. during the sealing process;        Any gases released during the sealing process should not contaminate the materials within the OLED display; and        The hermetic seal should enable electrical connections (e.g., thin-film electrodes) to enter the OLED display.        
Today, one way to seal the OLED display is to form a hermetic seal by softening a low temperature frit doped with a material that is highly energy absorbent at a specific wavelength of light to bond two substrate plates together. In particular, the frit is deposited on a substrate plate in a closed pattern, hereinafter the “frit pattern”, and a laser is used to heat up and soften the frit which forms a hermetic seal between the substrate plate or cover glass plate with the frit located thereon and a substrate plate or glass plate with OLEDs located thereon.
A problem which can occur in an OLED formed by the conventional laser heating of frit is the creation of residual stress, i.e., stresses remaining in the seal after the seal has cooled, in the frit seal at the location where the laser enters/exits the frit pattern during sealing, i.e., the frit pattern entry/exit point(s). This residual stress can lead either to a non-hermetic seal, resulting in an unusable product, or to premature failure of the seal, resulting in premature failure of the display. There is thus a need for a method of sealing a glass package which does not suffer from residual stress located at frit pattern entry/exit points. This need is satisfied by using one or more of the sealing techniques of the present invention.